If I purchase several season passes together do they have to be picked up together

different times

No you do not.

No you don't actually get them till you get to the gate.so get them register the ones you want then when the other party's get theirs they just show their kids and pick theirs up

No. If you purchase online, you can print the vouchers, and activate them as that person is able to go to the park. I bought 3 at one time, and activated one 3 weeks after the others.

No, you can get them at different times as long as you have the receipt for each card.

You should be able to pick them up at different times.